is in part what their genetic nature is, but it's also a part of what kind of an environment and life they live-- the nurture they have. so you can be genetically susceptible, but never exposed. but i think there's a public perception that the environment-- i mean smog, pesticides, water pollution, hair spray, you name it-- that these things are important causes of disease, and the reality is, they're not. there are a few biggies. there's cigarette smoke; there's asbestos... which is pretty much a problem of the past. and then, it's a pretty short list. the rest of the causes of disease are-- if they're not infectious-- are inside us. but often, the conditions in which one lives play a critical role in the ability to maintain good health, clearly, in most communities a level of development which has benefited many people, but left others behind. so one sees large slum areas of marginalized people, with people living under very poor conditions around the big cities. i saw it in china when i went there with my family in 1982. the farther away from beijing we went, the more "third world"